Endoskeleton- an internal skeleton, such as the bony or cartilaginous skeleton of vertebrates.
Exoskeleton- a rigid external covering for the body in some invertebrates animals, especially Arthropods, providing both support and protection.
A human hair is approximately 50 μm = 5 × 10⁻⁵ m in diameter
A trace gas is a gas which makes up less than 1% by volume of the Earth's atmosphere, and it includes all gases except nitrogen (78.1%) and oxygen (20.9%). The most abundant trace gas at 0.934% is argon.
Violet would refract the most as it has the shortest wavelength amongst the visible spectrum.